An eco-friendly vehicle is known as a vehicle that produces little or no pollutant compared with an internal combustion engine (ICE) vehicle that uses fossil fuel such as gasoline or diesel.
Recently, eco-friendly vehicles have received considerable attention due to issues of energy depletion and environmental pollution, and have already been commercialized or are about to be commercialized.
Most eco-friendly vehicles have been developed in the form of a vehicle that is driven by electric power, that is, a vehicle driven by using power of an electric motor.
Representative examples of the eco-friendly vehicle include a pure electric vehicle (EV) that is driven by operating a motor using power stored in a battery, a hybrid electric vehicle (HEV) that is driven using an engine (internal combustion engine) and a motor, and a fuel cell electric vehicle (FCEV) that is driven by operating a motor using power generated from a fuel cell.
Among above, an HEV refers to a vehicle that is driven by an engine for combusting fuel to generate driving force and a motor for generating driving force using electric energy of a battery and is known as a plug-in hybrid electric vehicle (PHEV) for charging a battery by inserting a plug into an electric outlet, a general HEV that does not perform this operation, and so on.
In addition, an HEV has been known to be configured with a power train using a transmission mounted electric device (TMED) in which a motor (driving motor) and a transmission are attached.
The HEV equipped with the TMED includes an engine and a motor as a driving source for vehicle driving, an engine clutch interposed between the engine and the motor, a transmission connected to an output side of the motor, an inverter for operating the motor, and a battery connected to the motor to be recharged or discharged through the inverter as a power source of the motor and is configured in such a way that the transmission is installed at the output side of the motor and the output side of the motor is connected to an input side of the transmission.
In addition, the HEV equipped with the TMED includes a motor connected to the engine for power transmission to turn on the engine or for generating power using rotation force transmitted from the engine, that is, a hybrid starter generator (HSG).
Among the above components, the engine clutch connects the engine and the motor to transmit power or disconnects the engine and the motor, and the inverter converts direct current (DC) of the battery into 3-phase alternating current (AC) and applies the converted current to the motor to drive the HSG of the motor.
The HEV including the above components is capable of being driven in an electric vehicle (EV) mode as a pure electric vehicle mode that uses only power of the motor, or a hybrid electric vehicle (HEV) that uses power of the engine and power of the motor in a multiple manner.
An eco-friendly vehicle such as an electric vehicle (EV) and a fuel cell electric vehicle (FCEV), which use a motor as a vehicle driving source, as well as a hybrid electric vehicle (HEV or PHEV) may execute a regenerative mode of charging a battery using a motor as a generator.
In other words, kinetic energy of a vehicle is converted into electric energy and is recovered during vehicle braking using brake equipment or during coasting in which a vehicle is driven using inertia.
In the regenerative mode, a motor that receives kinetic energy of a vehicle operates as a generator to recharge a battery connected to the motor through an inverter and, in this case, energy is capable of being recovered by the motor, thereby enhancing vehicle fuel efficiency.
In particular, when a deceleration event, for example an interchange (IC) or junction (JC), an intersection, a speed limit road, a curved road, a traffic light, a U-turn point, a left turn point, a right turn point, a tollgate, and destination, occurs in front of a road on which a vehicle is currently driven, the vehicle needs to be decelerated. When a driver pre-recognizes such a deceleration event and maintains an accelerator pedal and a brake pedal to be released at a time point requiring deceleration of the vehicle, the vehicle is driven using inertia (or coasting). In this case, it is possible to recover energy via coasting control, i.e., motor control for enabling a generation operation.
When a driver maintains brake pedal and acceleration pedal in an off state for deceleration in an eco-friendly vehicle, coasting of the vehicle is performed and, in this case, the vehicle is decelerated via control of torque (which is negative torque) of a motor without vehicle braking by brake equipment, and energy recovered by the motor is simultaneously stored in the battery.
Here, pedal off refers to a state in which a driver does not manipulate a corresponding pedal, that is, a state in which the driver takes their foot off the pedal (the pedal is released) and, on the other hand, pedal on refers to a state in which a driver pushes and manipulates a corresponding pedal.
Vehicle deceleration during coasting is similar to regenerative braking performed by pushing a brake pedal by a driver in that a battery is recharged via a motor. However, the vehicle deceleration during coasting is different from the regenerative braking in that regenerative braking is performed via braking force distribution into friction braking force by brake equipment and regenerative braking force (electric braking force) by a motor, while the vehicle deceleration during coasting is performed via only vehicle driving resistance and a motor without friction braking.
As such, an eco-friendly vehicle recovers vehicle energy as electric energy using a motor during braking or coasting, stores the recovered electric energy in a battery, and reuses the electric energy to drive the motor to increase driving distance and fuel efficiency of the vehicle, thereby effectively using energy.
Some hybrid electric vehicles that have been recently commercialized have a coasting guidance function of guiding and inducing coasting of a driver at an appropriate time when a deceleration event occurs in front of the vehicle.
The coasting guidance function is a function of operating an indicator, etc. of a cluster to induce coasting of a driver at a time when a vehicle is capable of being decelerated to target vehicle speed via coasting.
When a driver checks that coasting is possible via an indicator, etc., an accelerator pedal and a brake pedal are maintained in an off state to decelerate a vehicle to target vehicle speed at a target location of the deceleration event in a coasting state and, simultaneously, to recover energy by the motor during the coasting.
In general, most drivers take their foot off an accelerator pedal and push a brake pedal to decelerate the vehicle via brake equipment (friction braking equipment) when a deceleration event occurs in front of the vehicle.
In this case, the driver determines a time when their foot is taken off the accelerator pedal and a time when the brake pedal is pushed, with the naked eye and, in this case, actually, most drivers slowly take their foot off the accelerator pedal compared with a time corresponding to appropriate accelerator pedal off and, then, quickly manipulate the brake pedal to decelerate the vehicle and, accordingly, this may be very disadvantageous in terms of driving distance and fuel efficiency compared with the case in which a deceleration effect is obtained via only coasting.
On the other hand, an eco-friendly vehicle such as an electric vehicle, a hybrid electric vehicle, and a fuel cell vehicle is capable of performing torque control on a motor for driving a vehicle, that is, a driving motor and, thus, may achieve a similar deceleration effect of an internal combustion engine (ICE) vehicle using an automatic transmission via torque control (coasting motor torque control) of a driving motor during coasting.
The vehicle is smoothly decelerated to target vehicle speed while recovering maximum energy without brake manipulation via motor torque control only when a driver pre-recognizes a front deceleration event with the naked eye and, then, takes their foot off an accelerator pedal without manipulation of a brake pedal at an appropriate time.
When a vehicle is decelerated by manipulating a brake pedal rather than being decelerated via only coasting, friction braking using a brake and regenerative braking using a motor are distributed to ensure total braking force and, accordingly, it is possible to recover energy only when distributed regenerative braking is limited, which is disadvantageous in terms of enhancement in driving distance and fuel efficiency.
Accordingly, it is advantageous to decelerate a vehicle via only coasting without manipulation of a brake if possible to decelerate the vehicle to target vehicle speed from current speed and, to this end, it is important to guide a driver to take their foot off an accelerator pedal to cause coasting at an appropriate time.
In the case of an eco-friendly vehicle, it is possible to adjust deceleration force of the vehicle using a driving motor during coasting. Thus, when a driver drives the vehicle in an accelerator pedal and brake pedal off state via coasting, the vehicle is decelerated to target vehicle speed at a desired location by adjusting deceleration force using the driving motor while using friction force of the vehicle without manipulation of brake equipment. Accordingly, this is advantageous in terms of enhancement in driving distance and fuel efficiency compared with the case in which the accelerator pedal is slowly released at an appropriate time to brake the vehicle using brake equipment.
Replacement frequency of brake equipment is advantageously increased.
As such, in the case of an eco-friendly vehicle, when the vehicle is decelerated to target vehicle speed from current vehicle speed, it is advantageous in that vehicle deceleration via coasting is maximally used without manipulation of a brake to enhance driving distance and fuel efficiency.
To this end, there is a need for a coasting guidance and induction function of guiding drivers to take their foot off an accelerator pedal at an appropriate time.
However, a conventional coasting guidance function is mainly concentrated on determining expected vehicle speed to a target location of a deceleration event location from a current vehicle location and a start time of coasting based on a current vehicle state, a road condition, and so on, and guiding a driver to start coasting at the determined start time.
Accordingly, it is not possible to actively control a vehicle and, thus, there are various problems in that the coasting guidance function is inevitably limited, and it is difficult to maximize an effect of enhancing fuel efficiency due to low accuracy and reliability of control for coasting and guidance.
In addition, a logic for guidance of coasting is very complicated and a map value needs to be mapped to an input parameter based on a test value obtained via an advanced test in order to previously write and set a map for determining expected vehicle speed and so on and, accordingly, it is disadvantageous that errors are greatly increased when an environment change is changed and much time is consumed for mapping.